Certain radioactive materials emit particulate matter, namely alpha and beta particles that may be detected, identified, and quantified based on the measurement of the amount and energy of the alpha and beta particles emitted by the material containing the radioactive material. The emitted particulate matter may pose a hazard to humans through, for example, respiratory inhalation and/or ingestion. Various sampling systems are used to monitor for the presence of these particulate matter.
One specific alpha-emitting radioactive material is depleted uranium (DU). Depleted uranium has both military and civilian applications. Depleted uranium is uranium with a lower content of U-234 and the fissile isotope U-235 than is found in naturally-occurring uranium. Specifically, naturally-occurring uranium contains about 0.72 percent of the fissile isotope U-235, while the DU used by the U.S. Department of Defense contains 0.3% U-235 or less, as shown in Table 1.
TABLE 1Summary of the Table of Isotopic Abundances of DUTypicalCommercialFeedDepletedNaturalEnrichmentUraniumSpecific(mass(mass(massActivity IsotopeFraction)fraction)Fraction)(Ci/g)U-23899.2097.0199.803.3E−7U-2350.72 2.960.202.1E−6U-2340.00556.2E−30.00076.2E−3From DOE-STD-1136-2004 (DOE 2004)
Natural uranium has a specific activity of 0.68 pCi/μg, while DU has a specific activity that is about 60% of this value (see first page of the Overview section of Rostker 2000) (citations to references are provide in footnotes and/or at the end of this disclosure). Also, as described in Section 3 of Rostker, DU could contain trace levels of neptunium, plutonium and americium if the original source of the DU is recycled uranium from reprocessing spent reactor fuel. However, these radionuclides are in such trace quantities as compared to U-238 they do not require explicit consideration in assessing the doses and risks associated with inhaled or ingested DU.
Depleted uranium is useful primarily because of its high density, on the order of 19.1 g/cm3, as compared to the density of lead, 11.34 g/cm3. Civilian DU applications include counterweights in aircraft, radiation shielding in medical radiation therapy and industrial radiography equipment, and containers for transporting radioactive materials. Military DU applications include armor plating and armor-piercing projectiles.
Most DU is a by-product of the production of enriched uranium for use as fuel in nuclear reactors and in the manufacture of nuclear weapons. Enrichment processes generate uranium with a higher-than-natural concentration of lower-mass-number uranium isotopes (in particular U-235, which is the uranium isotope supporting the thermal fission chain reaction) with the bulk of the feed ending up as DU, in some cases with activity fractions of U-235 and U-234 less than a third of those in natural uranium. Since U-238 has a much longer half-life than the lighter uranium isotopes, DU emits less alpha radiation than natural uranium (i.e., about 40% less). Depleted uranium also arises from nuclear reprocessing; DU from this source has isotopic ratios different from enrichment-byproduct DU, from which it can be distinguished by the presence of U-236.
A large body of literature exists directed to DU issues; references from this body of literature cited herein are listed in detail at the end of this specification. The monograph, EPA 2006, provides an overview of the potential radiological and toxicological hazards associated with DU in the environment. Appendix 3 of the monograph provides a listing of the Superfund sites that are concerned, at least in part, with DU. Publications by the Wise Uranium Project, specifically “Current Issues—Depleted Uranium Weapons Tests and Incidents” (May 3, 2016) lists 21 sites where DU munitions have been or are being used in the U.S. The report also provides a summary of status reports of the issues associated with DU at individual sites and links to full text retrieval of the full reports (too numerous to describe here). In addition, a vast body of literature exists describing various physical and chemical forms of natural, depleted, and enriched uranium, and their associated radiological and toxicological hazards (see Cheng et al., 2009, ATSDR 2013, Parkhurst, et al., 2004, and Rostker, 2000). The literature describes the use of uranium and DU in a variety of commercial products, weapons systems, munitions, and as a byproduct associated with the development and production of the atomic bomb. Because of its widespread production and use, DU is ubiquitous throughout the world, and there is concern that it might represent both a radiological and toxic chemical hazard to individuals who might inhale or ingest DU under a number of conditions and settings, including:                1. Exposures to cleanup workers and members of the public during remediation of contaminated sites and facilities,        2. Exposures to members of the public exposed to DU in soil where legacy DU is present in soil,        3. Exposure of military and contractor personnel at facilities where munitions are tested, and        4. Exposure to military personnel during battle and also first-responders; i.e., those military personnel first on the scene (who were not in the vehicle) who help with vehicle and equipment evacuation, including battle damage assessment teams).1 1 See Committee on Toxicologic and Radiologic Effects from Exposure to Depleted Uranium During and After Combat, Committee on Toxicology, Board on Environments Studies and technology, Division on Earth and Life Sciences. National Research Council, The National Academy Press, Washington D.C., www.nap.edu.        
Many sites contaminated with natural uranium and DU are undergoing cleanup, where the soil and associated structures were contaminated with both natural uranium and DU. During cleanup, the natural uranium and DU may be resuspended and thus pose primarily an inhalation hazard to radiation workers and members of the general public. The literature provides some insight into the extent and concentration of DU in soil at selected sites. Hindin, et al, 2005 cited references that reveal that “In the United States there are over 50 sites that have been/are engaged in developing, producing, and testing DU munitions”. Crean, et al., 2013 explains, “when a penetrator strikes an armored target, 10-35% (maximum about 70%) of the mass is converted into aerosol with median aerodynamic diameter of d<15 micron.” This material disperses in the atmosphere and eventually deposits on nearby soil.
The following are examples of literature where the concentration of DU in soil at test sites have been reported:                Crean et al., 2013 describes the DU concentration in soil collected to a depth of 15 cm at Eskmeals in Cunbria, NW England, a Ministry of Defense (MOD) firing range that was used in the development and testing of DU weapons from the 1960s to 1995. The observed concentration of DU in surficial soil observed at different locations ranged from 37 to 320+/−40 mgU/kg (or about 10 to 100 to pCi/g).        Choy et al., 2005 reports concentrations of DU in surficial soil at U.S. Army sites of 3.99E3 Bq/Kg (1077 pCi/g), and that 83 percent of the DU is in fines (<0.075 mm or <75 microns) in which the DU concentration was 9.61E4 Bq/kg (2595 pCi/g) (note that natural background concentrations were reported as ranging from 1.7 to 2.2 mg/kg (i.e., 1.1 to 1.5 pCi/g) This concentration of naturally occurring uranium in soil is commonplace throughout the world. Table 25 of UNSCEAR 1993 summarizes the concentrations of naturally occurring Th-232 and U-238 in heavy mineral sands in Australia, reporting average concentrations in soil and rock for both Th-232 and U-238 of 40 Bq/kg or 1.08 pCi/g).        
The residual concentrations of DU in soil at battlefields have also been cited as follows:                Besic et al., 2017 reports soil concentration of DU in the Balkans at Hadzici and Han Pijsak in Bosnia and Herzegovina. The highest report activity of DU in soil at these battle ground sites range from 1024 Bq/kg (26 pCi/g) to 255,871 Bq/kg (6,909 pCi/g).        Mohammed 2008 presents a review of DU contamination in soil and its depletion and dispersion in the southern part of Iraq (Nassireya and Amara). In 2003, the DU concentrations in surface soil at 3 sites ranged from about 16 ppm (about 6.4 pCi/g) to 6 ppm (about 1.2 pCi/g). By 2007 the higher concentrations declined by about 25%, believed to be primarily by wind.        Sarap, et al., 2014 reports the concentration of U-238 soil samples collected to a depth of 10-15 cm in southern Serbia at locations where DU penetrators were used and following cleanup of left over DU fragments by NATO. The observed U-238 concentrations in soil samples reported in Table 1 of the report ranged from 21 to 95 Bq/Kg (0.57 to 1.3 pCi/g of soil), which is consistent with values reported in the literature, also in Table 1 of the paper. These values are quite low and likely do not represent a radiological or toxicological hazard.        
The assessment of the potential radiological and toxicological health risks at such sites, whether the sites are occupied or undergoing remediation, requires measuring the concentration of both natural uranium and DU in soil, air, and water. The health risks are primarily due to inhalation and ingestion of the different chemical and physical forms of uranium and DU. However, following an accident or during battle, relatively large fragments of DU can become imbedded in a person, and serve as a source of chronic DU dissolution into body fluids and the blood stream and deposition into organs of the body, such as the kidney and liver. Section 3 Part 5 of Rostker 2000 and also the latest update of Current Issues-Depleted Uranium Weapons Tests and Incidents (last updated May 3, 2017) present excellent overviews of issues and health effects associated exposure of military personnel to DU.
Parkhurst, et al., 2004 provides a comprehensive (627 page) report on aerosols of DU produced during testing of DU munitions used on Abrams tanks. A key finding of the report is that the airborne concentration inside armored vehicles following DU penetrator penetration ranged from 16 g/m3 (16,000 mg/m3) at 10 seconds after penetration to 0.029 g/m3 (29 mg/m3) one hour after penetration. An example of the time dependent airborne concentrations in the vehicle following penetration is provided in FIG. 5.5 in Parkhurst, et. al., 2004 is in FIG. 18. The particle size distribution of the aerosols as a function of time following penetration ranged from a fraction of 1 AMAD (activity median aerodynamic diameter) at time 0-30 sec to about 100-micron AMAD after several hours following penetration.
The implications of FIG. 18 are that the concentrations of DU, both in terms of radioactivity and micrograms per cubic meter are both high and rapidly changing. This figure serves as a good example of the conditions that the CAM 10 might encounter and how the software controlling the air sampling and counting will continually and automatically self-adjust in order to ensure that reliable alpha counts, representative of the airborne concentration in real time, are obtained. The key to ensuring the accuracy and reliability of the continuous measurements of airborne DU under circumstances such as those described in FIG. 18 is to ensure that the amount of particulates (primarily DU) deposited on the filter does not exceed a level that could result in the self-attenuation of the alpha emissions from the DU deposited on the filter. Specifically, in other sections of this application, it is demonstrated that, as that thickness of the particulate material deposited on the filter approaches 1E-3 cm, the potential exists for alpha self-attenuation. Assuming the airborne concentration of DU is at the high end of the distribution in FIG. 18 (i.e., 1E6 micrograms per m3) and the air flow rate is 10 L/min, the amount of DU deposited on the filter in one minute would be 10,000 micrograms (1E6 micrograms/m3×10 L/min×1E-3 m3/L). Since the area of the filter is 450 mm2, and assuming the density of the loosely deposited DU oxide on the filter, along with other airborne particulate material that may be present, is about 2 g/cm3, the thickness of the particulates on the filter would be 1×10-3 cm; about the thickness that could significantly attenuate the alpha emissions from the DU on the filter (1E4 micrograms/450 mm2×100 mm2/cm2×0.5 cm3/g×1E-6 g/microgram=0.0011 cm). Since the software controlling the air flow rate and duration of the airflow passing through the filter is continually being monitored, along with the airborne particulate concentration, the software will continually estimate the amount and thickness of the particulates on the filter. The software will continually adjust the flow rate and air sampling duration to ensure that the amount of particulates on the filter never reaches a point where the alpha emission from the DU on the filter will be substantively self-attenuated. Such a thickness will be empirically determined, but will initially be established at 1E-4 cm. When this thickness is reached, the filter will be moved from the sample collection location to the sample counting location, and a new filter will be moved to the sample collection location. These operational controls are referred to as a genetic algorithm.
During typical remediation efforts, both natural uranium and DU are monitored using methods that involve collecting samples and bringing the collected samples to a laboratory for analysis. A wide variety of techniques for the measurement of natural uranium and DU in solid and liquid samples have been developed and have been validated by many standards setting bodies. In addition, many laboratories are accredited for the performance of such analyses (DOE 2004 pg. 6-18).
In addition to DU that is resuspended at legacy sites during occupancy or remediation, there is also a potential issue associated with outdoor testing of munitions and armor and the generation of airborne plumes of DU at the time of such testing. This topic was investigated in depth in the Capstone Depleted Uranium Aerosol Characterization and Risk Assessment Study (Holmes et al. 2009). The Capstone Study was initiated following the 1991 Gulf War (Operation Desert Storm). Although the investigations addressed DU aerosols inside armored vehicles, the data provide some insight into the anticipated characteristics of the aerosols of DU outdoors in the vicinity of these munitions tests. The data include airborne concentrations of DU particles, particle size distribution (an approximation of activity medium aerodynamic diameter—AMAD, which is the value of aerodynamic diameter for which 50 percent of the airborne activity in a given aerosol is associated with particles smaller than the AMAD, and 50 percent of the activity is associated with particles larger than the AMAD) and particle chemistry as a function of time inside the test vehicles. A review of the papers reveals that the airborne concentration of uranium inside the test vehicles within a few minutes after impact was between 1E4 to 1E5 μg/m3 and remained at that level for at least two hours (Holmes, et al., 2009). The particle size distribution was found to be one micron AMAD at the end of two hours after the test (Cheng et al., 2009), and the aerosols quickly converted from the VI to the IV valence state; i.e., relatively soluble to highly insoluble (Krupka et al., 2009).
Because of concern regarding the exposure of workers during munitions testing and the possibility of fires associated with oxidation of uranium during testing (uranium metal is highly pyrophoric), such tests are now usually performed indoors and in other enclosures that minimize the potential for DU oxide aerosols to become airborne outdoors. However, it is often necessary for personnel to enter such enclosures shortly after testing in order to evaluate the performance of the munitions. Workers must wait until the airborne concentrations of DU aerosols decline before entry, and it is desirable to monitor DU prior to, during, and following entry into these enclosures. Such workers also often wear respiratory protection (which impedes worker efficiency to a degree). In addition, breathing zone samples and bioassay measurements are often made after the fact to ensure that worker exposures are maintained below radiation protection standards and as low as is reasonable achievable.
Depleted uranium munitions are also tested in a manner where they are fired but not detonated for the purpose of testing range and trajectory. In dry environments, such as in western regions of the U.S., DU penetrators oxidize on the firing range and can become aerosolized; again, posing a potential radiological and toxicological inhalation hazard.